Darstellung und Bildungsmechanismus von π‐Cyclopentadienyl‐nickel‐(tert.‐phosphit)‐dialkylphosphonat‐Komplexen – eine metallorganische Variante der Michaelis ‐ Arbuzov ‐Reaktion

Synthetic routes for complexes of the type π‐C 5 H 5 Ni[P(OR) 3 ]X have been developed. Nickelocene reacts with tertiary phosphites P(OR) 3 in the presence of CX 4 to give the complexes for which R = Me, Ph; X = Cl, and R = Ph; X = Br. π‐C 5 H 5 Ni(CO)I reacts with P(OR) 3 to give the complexes for which R = Me, Et, Ph. [π‐C 5 H 5 Ni(P(OMe) 3 ) 2 ]Cl is also formed in the preparation of π‐C 5 H 5 Ni[P(OMe) 3 ]Cl from nickelocene; the corresponding [π‐C 5 H 5 Ni(P(OEt) 3 ) 2 ]I is obtained from π‐C 5 H 5 Ni[P(OEt) 3 ]I and P(OEt) 3 . π‐C 5 H 5 Ni[P(OMe) 3 ]X (X = Cl, I) react with P(OMe) 3 to give π‐C 3 H 5 Ni[P(OMe) 3 ] [P(O)(OMe) 2 ] in quantitative yields, but with P(OEt) 3 and P(OPh) 3 π‐C 5 H 5 Ni[P(OEt) 3 ] [P(O)(OMe) 2 ] respectively π‐C 5 H 5 Ni[P(OPh) 3 ] [P(O)‐(OMe) 2 ] are obtained as the main products. The complex ( t ‐C 4 H 9 C 5 H 4 )Ni[P(OMe) 3 ] [P(O) (OMe) 2 ] can be synthesized by the same route. The course of the reactions of π‐C 5 H 5 Ni[P(OR) 3 ]X and P(OR′) 3 has been investigated in some detail. Intermediate compounds {C 5 H 5 Ni[P(OR) 3 ] [P(OR′) 3 ]X} with a π‐bonded cyclo‐ pentadienyl ligand have been detected at low temperatures by 1 H‐ and 13 C‐NMR.‐spectroscopy. They are stable up to about −10° and react at higher temperatures smoothly to π‐C 5 H 5 Ni[P(OR) 3 ] [P(O) (OR′) 3 ] and R′X. The structure proposed for the intermediates suggests that the mechanism of formation of the nickel phosphonate complexes is quite similar to that of the Michaelis ‐ Arbuzov reaction.